Pelvis & Perineum — Reproductive, Urinary & Pelvic Structures

🟢 Lite — Quick Review (1h–1d)

Pelvic Girdle — Bones & Joints

• Formed by: 2 hip bones (os coxae) + sacrum + coccyx
• Each hip bone: ilium, ischium, pubis ( meet at acetabulum)
• Acetabulum: socket for hip joint; lunate surface; acetabular notch (inferior gap)
• Obturator foramen: largest foramen in body; covered by obturator membrane
• Pelvic joints: sacroiliac (synovial + strong ligaments), pubic symphysis (fibrocartilaginous), sacrococcygeal
• Pelvic brim (inlet): divides pelvis into greater (false) and lesser (true) pelvis
• Clinical: Pelvic fractures — high-energy trauma; risk of hemorrhage from iliac vessels; “open book” fracture (symphysis diastasis)

Pelvis — Differences Between Male & Female

Feature	Male	Female
Overall shape	Narrower, deeper	Wider, shallower
Pelvic inlet	Heart-shaped	Oval
Pelvic outlet	Smaller	Larger
Subpubic angle	<90° (V-shaped)	>90° (U-shaped)
Sacrum	Longer, more curved	Shorter, flatter
Ischial tuberosities	Inward	Everted
Pre-auricular sulci	Shallow/absent	Deep in multiparous

• Clinical: Pelvic measurements (diagonal conjugate, obstetrical conjugate) important for cephalopelvic disproportion; female pelvis adapted for childbearing

Urinary Bladder

• Retroversical in males; retroperitoneal
• Trigone: smooth triangle between ureteral orifices (posterior) and internal urethral orifice (anterior); clinically important — infection starts here
• Detrusor muscle: smooth muscle of bladder wall
• Clinical: Bladder cancer — TCC (transitional cell carcinoma) most common type; suprapubic cystostomy for catheterization if urethral injury; bladder extrophy (failure of anterior wall to close)

Ureter — Pelvic Part

• Enters pelvis at bifurcation of common iliac artery ( at L5 level)
• Runs on lateral pelvic wall → anterior to internal iliac artery → turns medially at level of ischial spine → enters bladder posterolaterally
• 3 points of anatomical narrowing ( stone impaction sites): PUJ (pelviureteric junction), pelvic brim, intravesical portion (behind bladder wall)
• Clinical: Renal colic from ureteric stones — pain radiates from loin to groin; hematuria; hydroureter if obstruction

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🟡 Standard — Regular Study (2d–2mo)

Male Reproductive System

Testis & Epididymis:

• Sperm production (spermatogenesis) in seminiferous tubules; Leydig cells (testosterone) in interstitium
• Blood supply: testicular artery (from aorta below renal artery), deferential artery (from superior vesicle), cremasteric artery (from inferior epigastric)
• Clinical: Testicular torsion — “bell clapper” deformity (abnormal tunica vaginalis attachment); epididymitis (STI in young, E. coli in elderly); varicocele (dilated pampiniform plexus — bag of worms — may cause infertility)

Spermatic Cord:

• Contents: vas deferens, testicular artery, deferential artery, pampiniform plexus of veins, genital branch of genitofemoral nerve, lymphatics
• Coverings: external spermatic fascia (from external oblique), cremasteric fascia (from internal oblique), internal spermatic fascia (from transversalis)

Prostate Gland:

• Retrovesical (base of bladder); surrounds prostatic urethra
• Zones: peripheral (70% — where most cancers arise), central, transitional (BPH zone), anterior fibromuscular
• Clinical: BPH (benign prostatic hyperplasia) — transitional zone enlargement → lower urinary tract symptoms (hesitancy, weak stream, nocturia); PSA (prostate-specific antigen) — elevated in BPH and prostate cancer; radical prostatectomy — risk of urinary incontinence and erectile dysfunction

Penis:

• 3 erectile bodies: 2 corpora cavernosa (dorsal), 1 corpus spongiosum (contains urethra, expands into glans)
• Fascia: Buck’s fascia (deep) + Colles’ fascia (superficial — continuous with Scarpa’s fascia of abdomen)
• Blood supply: internal pudendal artery (main); superficial and deep dorsal veins (drain to internal pudendal → internal iliac)
• Innervation: somatic (pudendal nerve — S2–S4) for sensation and erection; autonomic (pelvic splanchnics — parasympathetic for erection, sympathetic for ejaculation)

Female Reproductive System

Ovary:

• Attached to uterus by ovarian ligament; suspended by suspensory ligament (contains ovarian vessels)
• Blood supply: ovarian artery (from aorta) + uterine artery (branch)
• Histology: cortex (follicles at various stages) + medulla (connective tissue + vessels)
• Clinical: Ovarian torsion (sudden severe pelvic pain, vomiting); ovarian cancer (most lethal gynecological cancer — often presents late); endometriosis (ectopic endometrial tissue — cyclical pain, dysmenorrhea, dyspareunia)

Uterus:

• Fundus, body, isthmus, cervix; pear-shaped
• Ligaments: broad ligament (peritoneum), round ligament (anterior), uterosacral ligament (posterior — contains autonomic nerves), cardinal ligament (lateral — contains uterine vessels)
• Support: pelvic diaphragm (levator ani) + perineal body
• Clinical: Uterine prolapse (grades I–IV — cervix protrudes through vaginal opening); fibroids (leiomyomas — most common benign tumor); endometrial cancer (postmenopausal bleeding is red flag)

Pelvic Fascia & Spaces

• Pelvic fascia: parietal (lines pelvic walls) and visceral (covers organs)
• Rectouterine pouch (of Douglas): lowest point in peritoneal cavity in females — clinically important for pooling of blood/pus
• Paravesical space: anterior to bladder
• Presacral space: between rectum and sacrum

Perineum — Boundaries & Divisions

• Diamond-shaped region bounded by pubic symphysis (anterior), ischiopubic rami (anterolateral), ischial tuberosities (lateral), sacrotuberous ligaments (posterior), tip of coccyx (posterior)
• Urogenital triangle (anterior): contains external genitalia and urethra (both sexes); covered by superficial perineal fascia (Colles’ fascia in males — continuous with Scarpa’s and dartos)
• Anal triangle (posterior): contains anal canal, external anal sphincter, ischiorectal fossae, pudendal canals
• Perineal body: fibromuscular node in center; anchors pelvic floor; important in obstetric trauma

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🔴 Extended — Deep Study (3mo+)

Pelvic Viscera — Rectum & Anal Canal

Rectum:

• 12 cm long; has 3 transverse folds (Houston’s valves — Kohlrausch’s valves)
• Peritoneal covering: only upper 2/3 anteriorly covered by peritoneum
• Blood supply: superior rectal artery (from IMA), middle rectal artery (from internal iliac), inferior rectal artery (from internal pudendal)
• Venous drainage: superior rectal → inferior mesenteric → portal; middle and inferior rectal → internal iliac → systemic
• Clinical: Rectal carcinoma — spread above peritoneal reflection directly to liver; below — to lungs; hemorrhoidal plexus (portal-systemic anastomosis)

Anal Canal:

• 4 cm long; has internal and external sphincters
• Dentate (pectinate) line: junction of anal valves; mucocutaneous junction; watershed area — above (visceral, autonomic innervation) → pain-free; below (somatic, pudendal nerve) → pain-sensitive
• Columns of Morgagni: between dentate line and anal verge; contain anal glands (may form abscess/fistula)
• Clinical: Hemorrhoids — internal (above dentate line — painless, bleed); external (below dentate line — painful); anal fissure (painful tear — posterior midline most common); anal cancer (squamous cell carcinoma — HPV associated); fistulas (Goodsall’s rule for tract prediction)

Pelvis — Vascular & Nerve Supply

Internal Iliac Artery Branches:

• Anterior division: superior vesicle (deferens in males, uterine artery), inferior vesicle, obturator, uterine (female), middle rectal, internal pudendal, inferior gluteal
• Posterior division: iliolumbar, lateral sacral, superior gluteal

Pelvic Nerve Plexuses:

• Hypogastric plexus: superior (presympathetic from aortic plexus) and left/right hypogastric nerves
• Pelvic plexus: on lateral aspects of rectum; receives sympathetic (from hypogastric) and parasympathetic (S2–S4 — nervi erigentes)
• Rectal plexus: superior (portal), middle and inferior (systemic)

Pelvic Splanchnic Nerves (Parasympathetic):

• S2–S4; convey visceromotor (motor to detrusor, erectile tissue) and viscerosensory (bladder/rectal stretch sensation)
• Clinical: Damage during pelvic surgery → bladder dysfunction; spinal cord injuries S2–S4 → neurogenic bladder

Pelvic Autonomics — Clinical Correlation:

• Erectile function: parasympathetic (S2–S4) via cavernous nerves → nitric oxide → smooth muscle relaxation → erection
• Ejaculation: sympathetic (T10–L2) → emission (ejaculatory duct) + closure of internal urethral sphincter (prevents retrograde ejaculation) + rhythmic pelvic floor contraction (bulbocavernosus)
• Bladder emptying: parasympathetic (S2–S4) → detrusor contraction; sympathetic (T10–L2) → bladder neck closure (continence)
• Clinical: Erectile dysfunction workup (vascular, neural, endocrine, psychogenic); retrograde ejaculation (sympathetic dysfunction — semen enters bladder); premature ejaculation (parasympathetic insufficiency)

Ischiorectal Fossae:

• Paired spaces on either side of anal canal
• Boundaries: laterally (ischial tuberosity + levator ani), medially (anal canal + external sphincter), anteriorly (superficial perineal pouch), posteriorly (gluteus maximus)
• Content: fat (compressive padding), pudendal vessels and nerves (Alcock’s canal)
• Clinical: Ischiorectal abscess — untreated → fistula-in-ano (perianal infection tracking to skin); horseshoe abscess (both sides connected posteriorly)

Pelvic Fractures — Clinical Anatomy

• Acetabular fractures: posterior wall (most common), anterior wall, transverse, T-shaped, both-column
• Ilial fracture: usually high-energy; risk of hemorrhage
• Pubic rami fracture: common in elderly osteoporotic patients; may indicate underlying pathology
• “Open book” injury: symphysis pubis diastasis >2.5 cm; disruption of sacrospinous and sacrotuberous ligaments; significant hemorrhage
• Pelvic bleeding: venous plexus and iliac vessels are main sources; angiography and embolization for refractory hemorrhage

Obstetric Pelvic Measurements:

• Diagonal conjugate: pubic symphysis to sacral promontory (~12.5 cm); if <11.5 cm = contracted inlet
• Obstetrical conjugate: true conjugate = diagonal conjugate − 1.5 cm (~11 cm)
• Interspinous distance: between ischial spines (~10.5 cm); if <9.5 cm = midpelvic contracture
• Clinical: Trial of forceps requires adequate pelvic dimensions; CPD (cephalopelvic disproportion) — indication for cesarean section

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